1. Field of the Invention
The invention concerns a mammography apparatus with a compression unit, and a method for operating such a mammography apparatus.
2. Description of the Prior Art
Mammography is an x-ray examination of the breast with the goal of detecting tissue variations at an optimally early stage. By continuous improvement of the mammography method it is sought to generate x-ray images with high significance in order to differentiate benign tissue variations from malignant tissue variations. In conventional x-ray mammography, a single two-dimensional image of a breast is generated at a single projection direction. A disadvantage of such imaging is that, due to overlapping tissue layers, it is often very difficult to detect a malignant structure in the region of a breast tissue. In order to obtain a three-dimensional image of the breast tissue, a number of x-ray images of the breast are acquired from respectively from different projection directions. During the x-ray acquisitions, the breast is fixed in position and simultaneously compressed in a compression unit. With these x-ray acquisitions, a three-dimensional image data set is generated via an image reconstruction algorithm (also called a tomosynthesis algorithm). For example, this three-dimensional image data set includes a number of slice images respectively situated parallel to the surface of the x-ray detector. Tissue structures situated atop one another in the propagation direction of the x-ray beam can be detected with this image data set. For tomosynthesis, x-ray exposures of the breast are acquired in a limited angle range of, for example, +/−25 degrees, starting from an orthogonal line established at the x-ray detector. Due to the incomplete scanning that results from this—i.e. due to the x-ray images being acquired only from a limited angle range of the breast—reconstruction of a plane from the 3D image data set has only a limited resolution. The resolution in the direction of the central beam (known as the depth resolution) is reduced relative to the resolution in the planes orthogonal to this direction.